Compact door operator



Feb.25, 1969 Filed Oct. 27, 1966 5,2 35 62 6! a. w. TUCKER, JR 3,429,073

COMPACT DOOR OPERATOR INVENTOR BENJAMIN WHITEHEAD TUCKER JR BY MZWATTORNEY Feb. 25, 1969 a. w. TUCKER, JR 3,429,073

COMPACT DOOR OPERATOR Filed Oct. 27. 1966 L2 LLZIZCLOSE 56 TPEN.

Sheet 2 of3 I35 I54 I32 I I FIG. 6

INVENTOR I BY ATTORNEY Feb. 25, 1969 a.w 1'ucKER, JR 3,429,0

COMPACT DOOR OPERATOR Filed 001:. 27. 1966 Sheet INVENTOR BENJAMINWHITEHEAD TUCKER JR.

United States Patent 13 Claims ABSTRACT OF THE DISCLOSURE A closureapparatus including a support structure, a sliding door mounted on thestructure for lateral movement between open and closed positions, amotor for operating the door, switch means for controlling the motor, alocking plate rotatably mounted on the structure, a linkageinterconnecting the door and the locking plate for rotating the lockingplate in response to lateral movement of the door, and a locking armpivotally mounted on the structure and ang-ularly displaceable relativethereto to three selected positions to operate the switch means forrespectively unlocking and opening, unlocking and closing and lockingand closing the door.

This invention relates generally to operators for sliding doors andparticularly to a novel operator suitable for use where space is at apremium as it is in rapid transit cars.

A so-called sliding door, as the expression is usually used, denotes adoor which is opened or closed by a lateral motion, as contrasted with aswinging motion, whether the door actually slides or whether it travelson wheels, balls, or rollers. The cars of railway rapid transit linesare usually equipped with several such doors on each side to permitquick passenger transfer at each station and also with one at each endto allow passage between cars. The end doors are normally arranged formanual operation, while the side doors are usually provided with poweractuated mechanisms, called operators, for opening and closing themeither automatically or under the control of an attendant. In service,the doors and operators should have certain characteristics. Efiicientoperation requires that the doors open and close quickly. They shouldoperate smoothly without jarring or banging when fully opened or thefully closed position is reached. Provision must be made for preventinginjury to a passenger in the pathway of a closing door. The mechanismmust not be damaged if door closing is prevented by the presence of anobstruction. When fully closed, the door should be mechanically lockedand a signal indicative of this condition should be generated, whichsignal should persist only as long as the door remains mechanicallylocked. The operator should be compact because there is no room abovethe door for bulky machinery. It is preferred that the operator belocated entirely within the walls of the car so as to leave the interiorfree for the use of passengers. And, of course, the operator should besimple and inexpensive.

Many kinds of operators have been proposed in the past. Some have beenoperated by fluid pressure, others by electricity. None has beenentirely satisfactory.

It is a general object of the present invention to provide an improvedoperator for a sliding door.

Another object is to provide an operator having the desirablecharacteristics previously mentioned.

A more specific object is to provide a compact operator which can bemounted readily within the wall of the structure carrying the door.

Briefly stated, a preferred embodiment of the invention includes asliding door which is opened and closed by a linear electric motoracting directly between the door 3,429,573 Patented Feb. 25, 1969 andits supporting structure. A shaft mounted on the structure ismechanically interconnected with the door so as to be rotated back andforth by the opening and closing of the door. This shaft serves as theoperating shaft for a fluid cushioning device and also carries a lockingplate which cooperates with a pivoted locking arm to lock the door inits closed position. The door may be unlocked by energizing anelectromagnet which raises the locking arm out of locking position. Themotion of the arm actuates suitable signal and control switches.

For a clearer understanding of the invention, reference may be made tothe following detailed description and the accompanying drawing, inwhich:

FIGURE 1 is a fragmentary elevation view of one side wall of a rapidtransit car taken from within the car with the interior panel removedand showing a sliding door equipped with an operator in accordance withthe present invention;

FIGURE 2 is an elevation view of the operator of FIGURE 1;

FIGURE 3 is a cross section view taken on the plane 3-3 of FIGURE 2;

FIGURE 4 is a schematic diagram of the electric control circuit;

FIGURE 5 is a schematic diagram of the timing circuit;

FIGURE 6 is a fragmentary elevation view of one end wallcf a rapidtransit car taken from within the car with the anterior panel removedand showing a sliding door equipped with an operator in accordance withthe present inventlon;

FIGURE 7 is an elevation view of the operator of F IG- URE 6;

FIGURE 8 is a cross section view taken on line plane 8- 8 of FIGURE 7;and

FIGURE 9 is a schematic diagram of the control circuit for the operatorof FIGURES 6, 7 and 8.

Referring first to FIGURE 1 there is shown a rapid transit car 21, theside of which is formed with an openmg which is alternatively covered orexposed by one or more sliding doors such as the door 22. These doorsare mounted for lateral movement by a conventional hanger arrangementthe details of which are not a part of the present invention.

A linear electric motor, designated generally by the reference character23, is provided for opening and closing the door 22. The motor 23comprises a magnetic assembly 24 fastened to the car and an elongatedconductive element 25 fastened to the edge of the door 22. The motor 23may be any of various kinds but in the specific embodiment beingdescribed it is a two phase linear induction motor which operates in amanner analogous tothat of the familiar squirrel cage motor. Themagnetic assembly 24 includes appropriate energizing windings forgenerating a linearly moving magnetic field.

A shaft 26 is rotatably mounted on the car 21. A crank arm 27 has oneend rigidly fastened to the shaft 26 and the other end pivotallyfastened to one end of a connect ing rod 28 the other end of which ispivotally fastened to the door 22. Accordingly, as the door is openedand closed by the motor 23, the connecting rod 28 and the crank arm 27cause the shaft 26 to rotate.

Referring now to FIGURES 2 and 3, there is shown a generally verticalmounting plate 31 which is formed with a vertically extending flange 32and a horizontally extending flange 33. The plate 31 is mounted withinthe wall of the car 21. As best shown in FIGURE 3, the wall of the carincludes an interior panel 34, an exterior panel 35 and a number ofcross pieces such as the cross piece 36. The plate 31 is mounted alongthe inside surface of the exterior panel 35 and is bolted to the crosspiece 36.

The previously mentioned magnetic assembly 24 is fastened to thehorizontal flange 33. The conductive element 25 is fastened to anL-shaped bracket 37 which in turn is fastened to the door 22. A roller38 is fastened to a bracket 39 which in turn is also fastened to thehorizontal flange 33 of the mounting plate 31. The roller 38 ispositoned to support and guide the conductive element 25.

A switch 41, sometimes referred to as the open limit switch (L) is alsofastened to the flange 33 and includes an actuator 42. The switch isoperated by an up-turned flange 43 of a bracket 44 which is fastened tothe movable element 25 in such a position that the switch is actuatedwhen the door 22 is in its fully open position as illustrated in FIGURE2.

The previously mentioned shaft 26 is the operating shaft of a hydrauliccushioning device 46 which is mounted on the plate 31. The device 46operates in a well-known manner to cushion the door 22 as it reaches itsfully open and fully closed positions. A locking plate 47 is rigidlyfastened to the shaft 26 and to the crank arm 27. The upper surface 48of the plate 47 is arcuate in form and concentric with the shaft 26, Thearcuate surface 48 is broader than the remainder of the plate in adirection parallel to the axis of the shaft, as best shown in FIGURE 3.The plate 47 is also formed with a radial abutment 49.

A locking arm 51 is pivotally mounted on the plate 31 by a shaft 52. Oneend of this arm, the right hand end, as viewed in FIGURE 2, has a lowercorner cutaway to form an abutment 53. The arm 51 is positoned above theplate 47 so that gravity urges the right hand end downward towardsengagement with the arcuate surface 48. A small roller 54 is mountednear this end of the arm and is the portion of the arm which actuallyrests on the surface 48.

An electromagnet 56 is mounted on the plate 31 just above the arm 51 andincludes a movable element which is connected to a link 57 which in turnis pivotally connected to the arm 51 so that this arm is raised when theelectromagnet 56 is energized. A switch 58, sometimes referred to as theclose limit switch (CL) is mounted on the plate 31 near the locking arm51. As best shown in FIGURE 3, the roller 54 is mounted on a stud 59which projects in back of the arm 51 so as to engage the actuator of theswitch 58. The opposite end of the locking arm 51, that is, the lefthand end as viewed in FIGURE 2, is formed with an extension 61 whichcarries two machine screws 62 and 63 which are positioned to engage theactuators of switches 64 and 65 which are mounted on the plate 31.

FIGURES 2 and 3 show the door 22 in its fully opened position. In orderto close the door, the magnetic assembly 24 is energized by a circuit tobe fully described subsequently. As the door closes, the connecting rod28 and the crank 27 rotate the shaft 26 and the locking plate 47clockwise. When the door is fully closed, the plate 47 will have rotatedto the dotted line position which is just far enough to allow thelocking arm 51 to drop down so that the two abutments 49 and 53 arejuxtaposed. Rotation of the Plate 47 in the counterclockwise directionis prevented, thereby locking the door closed, To open the door, theelectromagnet 56 is energized thereby raising the locking arm 51 abovethe surface 48 to a position higher than the position shown in FIGURE 2.Then the motor 23 may be energized and the door opened.

It is to be noted that the arm 51 can assume any one of three positons.The first, or raised position, occurs during the door opening when theelectromagnet 56 is energized to bring the arm 51 entirely out ofcontact with the surface 48. The second, or intermediate position,occurs when the electromagnet 56 is de-energized and the door 22 is inany positon except its fully closed position. At this time, the roller54 rests upon the surface 48 as shown in FIGURE 2. The third positon isa fully lowered position, which can occur only when the door 22 is fullyclosed and the electromagnet 56 is de-energized, so that the arm 51 candrop down to bring the abutment 53 opposite the abutment 49 so as tolock the door.

The switches 58, 64 and 65 are each capable of assuming either a firstor a second condition. The closed limit switch 58 is positioned andadjusted so that it assumes its first condition when and only when thearm 51 is in its third, lower position with the door locked. This switchis used in the control circuit as will be more fully explained.

The switch 64, although operated by the extension 61, is also positionedand adjusted so that it assumes its first condition when and only whenthe arm 51 is in its third position with the door locked. This switch isused as a signaling device and may be connected to either light orextinguish a lamp when the door is locked.

The switch 65 is positioned and adjusted so that it assumes its firstcondition when and only when the arm 51 is in its first or raisedposition. As soon as the electromagnet 56 is de-energized, dropping thearm 51 to its second position, the switch 65 assumes its secondcondition in which it remains as long as the arm 51 is in either itssecond or its third position.

Referring now to FIGURE 4, there is shown the elec tric circuit foropening and closing the door. Lines L1 and L2 are connected to asuitable alternating current source. The motor 23 is provided withterminals 71 and 72, bridged by a capacitor 74, and with a commonterminal 73 which is connected through a normally closed contact KIA tothe line L2. An adjustable resistor 75 is connected between line L1 andthe arm of the switch 65 which is a single pole double throw switch. Awarning lamp 76 has one terminal connected through the switch 64 to theline L1 and the other terminal connected to the line L2. A switch 77 isprovided to open and close the door. This switch may be operated eithermanually or automatically but for purposes of explanation it will beassumed that the switch is manually operated. A timing circuit 78includes the operating winding of a relay K1 which controls thepreviously mentioned contact KIA.

The remainder of the circuit can best be explained by considering itsmode of operation. FIGURE 4 shows the position of the parts when thedoor 22 is closed. The locking arm 51 is in its third position; theswitch 64 is in its first condition which is open and the lamp '76 isextinguished; the closed limit switch S8 is in its first condition whichis open; the open limit switch 41 is closed; and the switch 65 is in itssecond condition which corresponds to its upper position as shown in thedrawing. In order to open the door the switch 77 is moved to its openposition thereby energizing the electromagnet 56 and raising the lockingarm 51 to its first position. This closes the switches 58 and 64 andmoves the switch 65 to its lower position. Accordingly, the terminal 72is energized directly from the alternating current source while theterminal 71 is energized through the capacitor 74. The door 22 isopened, the switch 41 is opened, and the motor is de-energized.

In order to close the door the switch 77 is moved to its close positionthereby de-energizing the electromagnet 56, thus allowing locking arm 51to drop to its second position at which the roller 54 engages thesurface 48 of the locking plate as shown in FIGURE 2. This movement ofthe arm 51 raises the switch 65 to its up per position and, since theswitch 58 is closed at this time, the terminal 71 is energized directlywhile the terminal 72 is energized through the capacitor 74. The doorstarts to close. If no obstructions are encountered the door closesallowing the arm 51 to drop to its third position and lock the doorthereby opening the switch 58 and de-energizing the motor.

If an obstruction, such as a person, is in the path of the door it willbe prevented from closing. The torque of the motor has been limited byresistor 75 so that no injury to the passenger can result. However,continued energization of the motor may cause it to overheat. To preventsuch overheating, timer 78 is provided. If the door 22 does notcompletely close within a predetermined time after closing has beeninitiated, the timing circuit 78 operates to energize the relay windingK1 thereby opening the contact KIA and de-energizing the motor. Afteranother predetermined time, the winding K1 is de-energized therebyclosing the contact K1A, whereupon the motor 23 is again energized so asto close the door. This cycle of alternate energization andde-energization continues until the door is closed.

Rapid transit cars are usually provided with doors at each side but itis seldom that doors on both sides are opened simultaneously. Thereforea single timing circuit 78 can be used for the doors on both sides ofthe cars. Assuming, for example, that the motor 23 and door 22 areinstalled on the right hand side of the car, the left hand side isprovided with a motor 81 including terminals 82, 83 and 84 similarlyconnected. However, the same timing circuit 78 is also connected to theterminal 82 while the terminal 84 is connected to the terminal 73 sothat the timing circuit 78 is operative whenever either the right or theleft door is closed.

The details of the timing circuit 78 are shown in FIG- URE 5. Theterminal 71 and the line conductor L2 are connected to the inputterminals of a conventional full wave rectifier circuit 91 comprisingfour rectifying elements connected to the familiar bridge circuit. Thepositive output terminal is connected to a conductor 92 and the negativeoutput terminal is connected to a conductor 93. Two additionalrectifying elements 94 and 95 are connected to form alternative upperlegs of the bridge and provide a second input which is connected to theterminal 82. Thus, when either the terminal 71 or the terminal 82 isenergized with alternating current, a voltage appears on the conductor92 which voltage is positive with respect to the conductor 93.

The voltage on conductor 92 causes a current to flow through the lowvalve resistor 96 so as to charge a capacitor 97 quickly. A voltageregulating element such as a tube 98 is connected across the capacitor97 so as to hold the potential of the junction 101 substantiallyconstant. A conductor 102 is connected to the junction 101 and assumes apositive potential whenever either the terminal 71 or 82 is energized.Similarly, the junction 103, which is connected to the junction 102through a resistor 104, becomes positive with respect to conductor 93.

Three silicon controlled rectifiers 106, 107 and 108 are allnon-conducting initially because their gate electrodes are at the samepotential as their cathodes. The rectifiers 107 and 108 are connected ina conventional asymmetrical multivibrator circuit in which, when thecircuit is enabled, the two rectifiers conduct alternately. Therectifier 106 is connected in a circuit which enables the multivibratorafter a predetermined time.

Upon the appearance of a voltage at the junction 101, a current flowsthrough the resistors 111 and 112 and starts to charge the capacitor113. This circuit has a substantially longer time constant than theresistor 96 and capacitor 97 but eventually the potential of thecapacitor 113 rises sufficiently to cause a current to flow through theneon tube 114 and to render the controlled rectifier 106 conductive. Thejunction 103 falls quickly to substantially ground potential. Acapacitor 115 starts to charge through the resistors 116 and 117.Likewise a capacitor 121 starts to charge through the relay winding K1and a resistor 122. The circuit of capacitor 115 has a shorter timeconstant so that presently the potential thereof rises sufiiciently tocause the neon tube 123 to conduct thereby turning on the controlledrectifier 107. The multivibrator action almost immediately removes anypartial charge from the capacitor 121 through a resistor 124 and arectifying element 125. However, the capacitor 121 immediately starts tocharge again through the resistor 122.

Eventually the potential rises sufiiciently to cause the neon tube 126to conduct therefore turning on the controlled rectifier 108. The relaywinding K1 is energized, the contacts KIA (FIGURE 4) are opened, and themotor 23 is de-energized. At the same time the controlled rectifier 107is cut off and the capacitor starts to re-charge. Eventually, thecontrolled rectifier 107 is again turned on thereby turning off therectifier 108', de-energizing the relay K1 and closing the contact KIA.Thus the motor 23 is alternately de-energized and energized. The cyclerepeats until the door closes.

Reviewing the operation of the timing circuit, the motor 23 is energizedto close the door and if there is no obstruction it is de-energized bythe opening of the closed limit switch 58. If not so de-energized in apredetermined time, namely, the time required to charge the capacitors113, 115 and 121 successively, the contact K1A is opened therebyde-energizing the motor. After another predetermined time, namely, thetime required to charge the capacitor 115, the motor is re-energized.Then, after another predetermined time, namely, the time required tocharge the capacitor 122, the motor is again de-energized and the cyclerepeats until the door closes.

The operation has been described as occurring when the terminal 71 isenergized to close the door and this is correct. The timing circuit 78also starts to operate when the terminal 72 is energized to open thedoor. However, the door normally opens quickly and reaches its fullyopen position before the timing circuit 78 can operate. While it is notnecessary that the timing circuit operate during the opening of thedoor, such operation does no harm and actually provides additionalprotection to the motor.

The invention may also be applied to the end doors of a rapid transitcar, that is, to the doors through which one passes when going from onecar to another. As shown in FIGURE 6, the car 21 is provided withsliding doors 131 and 132 at each end. A linear electric motor 133comprising a magnetic assembly 134 including an energizing winding isfastened to the edge of the door 132. An elongated conductive element135 is fastened to the structure of the car. A shaft 136 is also mountedon the car structure and a crank arm 137 is rigidly fastened thereto. Aconnecting rod 138 has opposite ends pivotally fastened to the crank arm137 and to the door 132. Thus, the motor opens the door and the doorrotates the shaft 136-.

As best shown in FIGURE 7, a bracket 141 is formed with a generallyhorizontally flange 142 which is fastened the bottom of the magneticassembly 134. The bracket 141 is also formed with a generally verticalflange 143 which is fastened to the door 132. The conductive element 135is fastened to the car structure by means of a rubber block 144 whichalso serves as a resilient stop for the assembly 134 in case it shouldovertravel. A switch 146, also fastened to the car structure, includesan actuator 147 which is operated by a strap 148 fastened to the bracket141 in such a position as to actuate the switch 146 when the door is inits fully opened position as shown in FIG- URE 7.

As best shown in FIGURE 8, the end wall of the car 21 includes aninterior panel 151, an exterior panel 152 and two frame members orbraces 153 and 154. A rigid block 155 is fastened to the brace 153 andsupports a strong rigid plate 156 which in turn supports a mountingplate 157. As shown in FIGURE 7, a cushioning device 159 is fastened tothe plate 157 and carries the previously mentioned operating shaft 136to which the crank arm 137 is rigidly fastened. A locking plate 161similar to the plate 47 of FIGURES 2 and 3, is fastened to the shaft 136and the arm 137. A locking arm 162 is similar to the arm 51 except thatthe extension 163 on the left side may be formed slightly differently soas to accept two machine screws 164 and 165 side by side, which screwsoperate switches 166 and 167 respectively. These switches are bothactuated to their first condition when and only when the arm 162 is inits first, raised, position. A switch 168,

7 comparable to the switch 58 of FIGURE 2, is actuated to its firstcondition when and only When the arm 162 is in its third, loweredposition with the door locked. An electromagnet 169 is operativelyconnected to the arm 162 so as to unlock the door when energized in thesame way that the electromagnet 56 unlocks the door 22.

The end door 132 is operated a little differently from the side door 22.On the interior Wall of the car, adjacent to the door, is a push button.When this button is depressed, the door opens and remains open for apredetermined time after which it closes. The circuit for accomplishingthis is shown in FIGURE 9.

In FIGURE 9, the parts are shown in the positions they are in when thedoors are fully closed. When power is first applied to the alternatingcurrent lines L1 and L2, current flows from L1 through the switch 166and the rectifier 171 to the line L2. The relay winding K2, which isconnected to the output terminals of the rectifier 171, is energizedthereby closing the contacts K2A. A capacitor 172 is charged by beingconnected in series with resistors 173 and 174 and a rectifying element175 across the output of the rectifier circuit 171. The two resistors173 and 174 are of comparatively low value so that capacitor 172 cancharge quickly. The relay winding K2 is connected from one terminal ofthe capacitor 172 through a large resistor 176 to the junction of theresistors 173 and 174.

To open the door, the push button 181 is depressed momentarily therebyenergizing the electromagnet 169 and raising the arm 162 to its firstposition which closes the switch 168 and moves the switches 166 and 167to their first conidtion which is the opposite condition from that shownin FIGURE 9. The electromagnet 169 is maintained energized through acircuit including the switch 166 and the contacts K2A which are nowclosed. The operation of the switch 166 also removes the alternatingvoltage source from the rectifier 171, tending to de-energize the relaywinding K2. However, the capacitor 172 discharges through the resistors173 and 176 and the winding IQ thereby holding it energized for apredetermined time. At the same time, the motor 133 is energized throughan adjustable resistor 182 and the switch 147 so as to open the door.When the door is fully opened the switch 147 is opened therebyde-energizing the motor. Eventually the capacitor 172 becomes dischargedto such an extent that the relay winding K2 becomes de-energized therebyopening the contacts K2A which de-energize the electromagnet 169. Theswitch 167 is thereby moved to its upper position so that the motor 133is energized through the switch 168, which is now closed, therebyclosing the door. The capacitor 172 recharges quickly through therectifier 175 and the low value resistors 173 and 174. The apparatus isnow ready for another cycle of operation.

It is to be noted that in the embodiment described in connection withFIGURES 1, 2 and 3, the magnetic assembly of the motor is stationarywhile the conductive element moves. This arrangement is suitable whenthe hollow wall is very thin so that it is impossible to place the doorand the conductive element side by side. However, this arrangementrequires a substantial amount of clearance in the lateral direction. Asis apparent from FIGURE 1, when the door opens, the element moves asubstantial distance to the left but the door does not reach themagnetic assembly 24 which is in substantially the same plane as thedoor. In contrast, in the embodiment of FIG- URES 6, 7 and 8 there ismore room between the panels of the end wall but much less room in thedirection of door motion. These conditions lend themselves to the use ofa stationary conductive element and a movable magnetic assembly. Asshown in FIGURE 8, the door 132, when open, is behind both theconductive element 135 and the mounting plate 157.

From the foregoing description it is apparent that the present inventionprovides a simple operating mechanism for the doors of rapid transitcars which mechanism pro- 8 vides the necessary locking safeguards andwhich mechanism can be placed within the walls of the cars.

Although some preferred embodiments of the invention have been describedin considerable detail for illustrative purposes, many modificationswill occur to those skilled in the art.

What is claimed is:

1. Closure apparatus, comprising,

a structure,

a sliding door mounted on said structure for lateral movement betweenopen and closed positions, motive means for moving said door betweensaid open and closed positions,

switch means for controlling said motive means,

a locking plate rotatably mounted on said structure,

means interconnecting said door and said locking plate for rotating saidlocking plate about an axis of rotation in response to lateral movementof said door,

a locking arm pivotally mounted on said structure and angularlydisplaceable relative to said structure about a pivot axis to first,second and third angularly spaced positions, said locking arm beingoperative at said first position to operate said switch means to controlsaid motive means for opening said door and said locking arm beingoperative at said second position to operate said switch means tocontrol said motive means for closing said door and said locking armbeing operative at said third position to cooperate with said lockingplate for locking said door when said door is fully closed, and

means for angularly displacing said locking arm.

2. Apparatus according to claim 1 in which said locking plate is formedwith an arcuate surface and is formed with a first abutment disposed atone end of said surface,

said locking arm is formed with a second abutment and said locking armhas a roller rotatably connected therto, said roller being disposedadjacent said second abutment, and

said locking arm is mounted in such position that the force of gravityacting thereon urges said second abutment toward a position oppositesaid first abutment when said door is closed and urges said roller intoengagement with said arcuate surface while said door is being closed.

3. Apparatus according to claim 1 in which said means interconnectingsaid door and said locking plate includes a thrust member, and in whichsaid door has a central portion disposed between the top and bottomedges of said door that is connected to said thrust member.

4. Apparatus according to claim 3 in which said means interconnectingsaid door and said locking plate includes a crank arm rigidly fastenedto said plate, and in which said thrust member is a connecting rodpivotally connected at opposite ends to said crank arm and to thecentral portion of said door.

5. Apparatus according to claim 3 in which said motive means has aportion connected to and controlled by said switch means and a portionconnected to said door for moving said door between open and closedpositions.

6. Apparatus according to claim 5 in which said motive means is a linearelectric motor including first and second relatively movable members,one of said members being connected to said door adjacent to said thrustmember connection.

7. Apparatus according to claim 6 in which said first member is anassembly including energizing windings and said second member is anelongated conductive element, and in which said motive means has meansfor adjusting the driving force appled by said motive means to saiddoor.

8. Apparatus according to claim 7 in which said first member is fastenedto said door and said second member is fastened to said structure.

9. Apparatus according to claim 5 further comprising means jointlyresponsive to the elapse of a predetermined time after initiation ofdoor closing and to the location of said locking arm in said secondoperative position and said door in at least a partly opened positionfor alternately deenergizing and re-energizing said motive means.

10. Apparatus according to claim 5 further comprising manually operablemeans for energizing said motive means to open said door, and

means jointly responsive to the elapse of a predetermined time afterinitiation of door opening and to the location of said locking arm insaid second operative position for energizing said motive means to closesaid door.

11. Apparatus according to claim 6, including a rotary fluid cushioningdevice which has a shaft fixedly connected to said locking platecoaxially therewith and which serves to bring said door to a smooth stopas it approaches its fully opened and fully closed positions, andincluding an electromagnet having a movable element operativelyconnected to said locking arm, and including a mounting plate whichsupports said locking arm and cushioning device and electromagnet on oneside thereof :and which is supported by said structure.

12. Apparatus according to claim 11 in which said structure includes ahollow Wall formed with an interior and an exterior panel, said panelsforming a space therebetween in which said mounting plate is disposed,

said wall being formed with :an opening through both of said panels,

said door being mounted so as to at least partially cover said openingwhen in its closed position and so as to retract into said space betweensaid panels :and to be disposed adjacent to said mounting plate when inits open position.

13. Apparatus according to claim 6 in which said switch means includesfirst, second and third electric switches, all mounted on saidstructure, each capable of assuming either a first or a secondcondition, the condition of each being controlled by the position ofsaid locking arm in each of the three operative positions of saidlocking arm.

References Cited UNITED STATES PATENTS 1,715,505 6/1929 Klumpp 49-14 X1,976,223 10/1934 Hedley et al 4928O X 2,893,506 7/1959 Daugirdas 49'13X 2,895,728 7/1959 Edelman 49-30 X FOREIGN PATENTS 551,522 6/1932Germany.

I. KARL BELL, Primary Examiner. I DAVID J. WILLIAMOWSKY, AssistantExaminer.

U.S. Cl. X.R.

